Question

I have all way been bad at this stuff

Answer 1

Don't worry about not being good at this. Its really random and you will never need to know this.
a) 13-(-3) = 16 subtration
13+3 = 16 addition
b) An example of this would be -2 and 3.

Answer 2

A. Subtraction: 13 -(-3)=16
Addition: 13 +(-3)=10

B. 40*F and 45*F